Method for use in sampling and/or measuring in reservoir fluid

ABSTRACT

The invention relates to a method for use in sampling, flow measuring, quantity gauging, or possibly other analysis performed in reservoir fluid found in a ground formation. An object of the invention is to perform the sampling, flow measuring and quantity gauging or the remaining analyses in situ on stabilized reservoir fluid that contains a negligible amount drill fluid. Analysis is possible by sealing off an area of the well at the hydrocarbon carrying layer and passing a volume of reservoir fluid into a drill string for analysis by accessories located in the drill string. After the analyses are performed, the reservoir fluid is returned to the hydrocarbon carrying layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of the priority data ofNorwegian Application no. 19990344, filed Jan. 26, 1999, andInternational Application no. PCT/NO00/00020, filed Jan. 26, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for taking samples, makingflow measurements, quantity gauging, and possibly performing otheranalyses in reservoir fluid run into within a ground formation, forexample, when drilling an exploration well for hydrocarbons.

2. Prior Art

Use of new technology in, inter alia, drilling and production in groundformations exhibiting high pressure and temperature, injection of waterand gas for increasing the degree of extraction, multiphase productionon the seabed and transport of produced hydrocarbons in pipelines on theseabed, makes constantly ever greater demands on maximum knowledge aboutthe physical and chemical properties of the gas, oil and water to beproduced from the deposit. Previously, such knowledge about thereservoir fluid within the ground formation was normally provided bymeans of testing at complete production. However, today there is a cleartendency towards increased use of various sampling tools which, duringdrilling, are passed down into and pulled up from the well by means of awire string. The last mentioned method, however, gives fewerpossibilities to provide data about relevant parameters of the reservoirfluid than what is possible at full production testing.

Each of the above-mentioned methods has its different advantages andweaknesses. The strength of full production testing is that data can becollected in a large volume of the reservoir fluid, so that the databecome very reliable. The main weakness is the large expenses incurredupon, for example, renting a rig and other necessary accessories.Another significant deficiency is that it becomes necessary with one oranother form of handling of the large amount of reservoir fluidconducted up to the surface. Today, this takes normally place throughundesirable burning of the oil and gas.

Important advantages of use of sampling and measuring accessorieslowered down into the well by mans of a wire string, is that samples ofthe reservoir fluid can be taken continuously during the drilling, andthat this can take place with far less expenses than upon fullproduction testing. Nor is it necessary to burn oil and gas. The mainweakness of the accessory is, as already mentioned, the limitations inwhat the accessory can provide of data about relevant parameters for thereservoir fluid. For example, absolutely necessary data about theflowing conditions in the reservoir fluid can not be provided. Nor isthe accessory usable in connection with saturated gas reservoir aspressure and temperature can not be stabilized. The weakness isincreased further due to the fact that very small amounts of thereservoir fluid are taken out, and that the accessory has to be handledfrom the surface. Moreover, the last mentioned condition may result inthat the measuring results for the reservoir fluid become unreliable.Such errors in the measuring results may be due to, inter alia, the factthat the accessory is not brought into the correct position within thereservoir during the sampling; that the reservoir fluid where samplesare taken is contaminated with drilling fluid supplied during thedrilling, and that sand accompanying the reservoir fluid during thesampling causes leakage in the accessory.

BRIEF SUMMARY OF THE INVENTION

The above-described problems are solved by the present method. Thepresent method comprises sealing an area of the ground formation'shydrocarbon carrying layer and supplying reservoir fluid from thehydrocarbon carrying layer into a pipe string. Sampling and/or flowmeasuring, quantity gauging, and possibly other analysis are carried outin the sealed area of the well while the reservoir fluid flowscontrollably into the pipe string. The reservoir fluid is then returnedfrom the pipe string to the hydrocarbon carrying layer within the groundformation after completing the sampling and analysis.

A great advantage of the present method over prior methods is that thesampling, flow measurements, quantity gauging, or other analysis can becarried out in reservoir fluid positioned down within the hydrocarboncarrying layer. Such reservoir fluid is stabilized as much as possibleand, moreover, free of drill fluid.

The supply of reservoir fluid may be controlled by means of a downholevalve or a surface valve. A piston separates the reservoir fluid fromwater or N₂. Subsequent to perforation of the well, the piston movesupward when reservoir fluid is let in with a speed adjusted by means ofthe valve. Thus, the inflow of reservoir fluid can be measured byreading the amount of liquid (water or N₂) which, during the inflow, hasflowed into a tank at the surface. When the reservoir fluid has risen sohigh up in the string that the liquid has reached the security valve,often called the BOP, at the seabed or the surface, the piston isstopped by a seat. Then, all tests are carried out downhole, and thereservoir fluid is pressed back to the reservoir.

Uniform pressure data are achieved due to a stabilized inflow ofreservoir fluid into the pipe string. The sampling, flow measurements,quantity gauging or other analyses may be performed with an accessorywhich is available at any time, so that as much data as possible aboutthe reservoir fluid can be gathered. Trace elements, or tracers, may beadded to the reservoir fluid in order to carry out flow measurements,while still returning the reservoir fluid to the hydrocarbon carryinglayer from which it was taken.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe spirit and scope of the invention as set forth in the appendedclaims. The novel features which are believed to be characteristic ofthe invention, both as to its organization and method of operation,together with further objects and advantages will be better understoodfrom the following description when considered in connection with theaccompanying figures. It is to be expressly understood, however, thateach of the figures is provided for the purpose of illustration anddescription only and is not intended as a definition of the limits ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference isnow made to the following descriptions taken in conjunction with theaccompanying drawing, in which:

FIG. 1 is a view of a well containing a drill string equipped for insitu analysis.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to the figures, FIG. 1 shows a diagrammatic detail sectionwithin a lower portion of an exploration well which is in the course ofbeing drilled in a ground formation. The well is drilled by means of adrilling accessory comprising a bit located on a drill string. Thesampling, flow measuring and quantity gauging or the other analyses ofthe reservoir fluid are carried out by accessories positioned within ahousing member surrounding the drill string above the bit. The well issealed in an area at the hydrocarbon carrying layer of the groundformation by means of seals located externally on the housing member,and which are expanded to create a seal by resting against the wellwall. Examples of accessories for sampling, flow measurements andquantity gauging or other analyses are indicated in FIG. 1 by brokenlines.

Sampling, flow measurements, quantity gauging and possibly otheranalyses are performed in reservoir fluid found in a ground formation 1.Highly accurate measurements are achieved without bringing large volumesof reservoir fluids to the surface by sealing the well 3 in an area atthe hydrocarbon carrying layer 2 of the ground formation 1. Reservoirfluid from the hydrocarbon carrying layer 2 is supplied in a drillstring 4 which penetrates the sealed area of the well. The sampling, theflow measurements, quantity gauging and other analyses of the reservoirfluid are carried out in the sealed area of the well 3. Preferably, thistakes place after the drill string 4 is sealed and filled with reservoirfluid supplied thereto. Thus, the sampling and the respectivemeasurements or analyses take place after a larger amount of thereservoir fluid has been supplied into the drill string 4, thus enablingone to take samples or make measurements in reservoir fluid stabilizedafter the drilling and substantially lacking in drill fluid content.Inter alia, this is a result of the fact that the previously mentionedpiston separates the reservoir fluid from the above positioned water orN₂, and where said water or N₂ is used to press out drilling mud fromthe drill string and out into annulus.

After perforation, the piston will move upwardly within the drill stringwhen reservoir fluid is let into the drill string. After sampling andthe respective measurements are completed by means of sampling,measuring or analyzing accessories 9-12 which are lowered down into thewell 3 together with the drill string 4, the reservoir fluid is returnedfrom the drill string 4 to the hydrocarbon carrying layer 2 in theground formation 1 in a suitable way. Thereupon, the sampling, measuringor analyzing accessories 9-12 are pulled out from the well 3 togetherwith the drill string 4, so that the limited amount of reservoir fluidaccompanying the equipment up to the surface may be further appraised inthe laboratory. Thus, avoids the great burden of bringing a large volumeof reservoir fluid to the surface. Possibly, the drilling may becontinued downwardly towards the underlying layer, so that samples canbe taken and measurements or analyses may be made therein in acorresponding way.

Prior to the sampling, flow measurements and quantity gauging or theother analyses, a logging and washout of the well 3 normally will becarried out before the same is sealed. The washout can be made by meansof a washing agent which is circulated within the well 3. When reservoirfluid is supplied into the drill string 4, the drill fluid is circulatedthrough a suitable valve between the drill string 4 and the annulusformed between the well wall and the drill string 4, and drill fluid istransferred further from the annulus for storage in tanks, not shown, atthe surface. Thus, drill fluid is replaced by gas or liquid (N₂/water)prepared for the testing phase by adding a tracer, normally a traceelement. Above, it is mentioned that the sampling, flow measurements andquantity gauging or the other analyses in the reservoir fluid arecarried out continuously, and after the drill string has been filled ina controlled way with reservoir fluid by means of a downhole valve.However, this does not prevent that the sampling, flow measurements andquantity gauging or the other analyses can take place at anotherexpedient point of time. For example, this may be the case where it isdesirable to make continuous measurements while the reservoir fluid isbeing supplied into the drill string 4.

Further, in FIG. 1, an exploration well 3 is shown, drilled with a bit15 located on a drill string 4 and which, during drilling, is pressureequalized by means of drill fluid with the tracer added thereto. Thedrill string 4 may be a coiled tubing or its equivalent. Above the bit15, the drill string 4 is surrounded by a housing member 7 having alength preferably somewhat larger than the height of the hydrocarboncarrying layer 2 of the ground formation. The housing member 7 may bemade of steel having a high durability against an acidic environmentthat has a high content of chlorides. One end of the housing member 7 iscoupled to the drill string 4, possibly the bit 15, in a pressure-tightway. Moreover, the well 3 may be equipped with a casing 16 which eitheris terminated above the hydrocarbon carrying layer 2 or passed throughthe same. In the latter case the casing must be equipped withperforations or their equivalent at the layer 2.

The housing member 7 is equipped with expandable seals 5, 6 spaced apartfrom each other and located externally on the housing member 7, so thatthe well 3 can be sealed. Seals 5, 6 is placed at the upper and lowersides of the hydrocarbon carrying layer 2. Seals 5, 6 may be placed inalternate locations, for example merely at the central portion of saidlayer 2. The seals 5, 6 may be of any suitable type. The housing 7 iscentralized within the well 3 when the seals 5, 6 are expanded to restagainst the well wall in order to create the seal. The length of thehousing member 7 and the positioning of the seals 5, 6 are determined onthe basis of preceding seismic investigations in the ground formation 1.Moreover, the housing member 7 is equipped with at least one gate 8 orthe like, that may be opened so that the reservoir fluid can be suppliedinto or returned from the drill string 4.

Within the housing member 7, the drill string 4 is equipped with asuitable valve arrangement 13 which is adapted so that the reservoirfluid can pass into or out of the drill 4 string during the supply fromor the return into the ground formation 1, respectively. Further, theupper end of the drill string 4 is equipped with an upper valvearrangement 14 which is adapted so that the drill fluid may pass outfrom or into the drill string independently of whether the reservoirfluid is supplied into or returned from the drill string in the mannerpreviously described. The drill fluid is stored in tanks, not shown,while the reservoir fluid occupies the drill string 4. Moreover, theupper valve arrangement 14 is adapted so that the drill string 4 may beclosed when the level of reservoir fluid brought into the drill stringhas reached up to the upper valve arrangement 14 (e.g. a BOP) or anyother desired level in the drill string 4. A preferred means of closingthe valve or stopping the fluid is a piston, not shown, that is stoppedin a seat.

The housing 7 holds the accessories required for taking the samples andmaking the measurements necessary for charting relevant properties orparameters of the reservoir fluid. Said accessories for sampling andmeasuring are selected from the accessories which, at any time, areavailable on the market, and the housing member 7 may be equipped withother accessories for sampling and measuring than those described. Thesampling may be carried out by means of single-phase containers 9 foroil, gas and water. Temperature, pressure, content of H₂SO and SO₄,pH-conductivity, density, and C1-value, etc., can be measured by meansof a sensor-pipe string system 10. PVT-values (pressure, volume,temperature), IR (infrared radiation) can be measured by means of anacoustic resonance spectroscopy sensor system 11 (Acoustic ResonanceSpectroscopy Sensor system). In order to measure flow within thereservoir fluid, the housing member has accessory 12 for adding asuitable tracer for oil, gas and water into the reservoir fluid.Preferably, the tracer is added while the drill string 4 is filled withreservoir fluid and the upper valve arrangement 14 is closed.

Preferably, the housing member 7 is equipped with an acousticcommunication system, not shown, so that a higher number of sensorsystems for various types of measurements can be placed within thehousing member 7 in desired combinations. Said communication systemconsists of smaller and intelligent communication units coupled to thevarious sensors within the housing member 7. Thus, sensor data may betransmitted acoustically to a logging or telemetry unit on the surface,without the use of communication cable. This is favorable becausetransfer of signals by cable, due to the complexity of the sensors ormovable parts in the tool, normally is very problematic in tools havinga small diameter.

After completing sampling and measurements in the reservoir fluid, andreturning the reservoir fluid from the drill string 4 to the groundformation 1, the housing member 7 with the accessories 9-12 assignedthereto, is pulled up to the surface together with the drillingequipment. The equipment concerned is then disconnected from the housingmember 7 and brought to the laboratory, so that the reservoir fluid canbe analyzed further.

While the presently described embodiment comprises supplying into andreturning reservoir fluid from the drill string 4, cases may exist inwhich the present invention is adapted so that the drill string my besubstituted by a tubing string or a “testing” pipe string extendingalong the drill string 4 and, preferably, between the bit 15 and thevalve arrangement 14 at the surface. Further, cases may exist in whichit is more suitable that the housing member 7, in lieu of the shownpositioning down at the bit 15, is located further up on the pipestring. Likewise, multiple housing members 7 may be employed, eachhaving its own variety of accessories for sampling and measurements, sothat simultaneous samples and measurements may be taken from variouslayers in the ground formation 1.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, compositionof matter, means, methods and steps described in the specification. Asone of ordinary skill in the art will readily appreciate from thedisclosure of the present invention, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present invention.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

What is claimed is:
 1. A method for use in reservoir fluid measuringoperations, carried on as in situ measurements, comprising the steps ofsealing a well with a sealing means in an area at a hydrocarbon carryinglayer of a ground formation so as to create a sealed off area; extendingan elongated pipe string from a surface position downwardly into saidsealed off area; conducting reservoir fluid controllably through its owninherent pressure from said hydrocarbon carrying layer into said pipestring; carrying out said measuring operations in situ in the sealed offarea by using instrumentation attached to or contained within said pipestring; and returning the reservoir fluid from the pipe string to thehydrocarbon carrying layer after said measuring operations have beencompleted.
 2. A method as claimed in claim 1, wherein said measuringoperations comprise sampling, flow measurements, and quantity gauging.3. A method as claimed in claim 2, wherein said pipe string comprises agated housing member and the reservoir fluid is conducted into said pipestring through the gate located in said gated housing member.
 4. Amethod as claimed in claim 3, wherein the measuring operations arecarried out using a sensor.
 5. A method as claimed in claims 4, whereinthe gate is closed and opened by means of a valve arrangement located atthe upper end of the pipe string.
 6. A method as claimed in claim 4,wherein the respective output results from said sensor are converted andtransmitted to the surface by means of an acoustic communication systemlocated within the housing member.
 7. A method as claimed in claim 2,wherein said sampling, flow measuring, quantity gauging are carried outby means of sampling, flow measuring and quantity gauging accessorieslocated within a housing member.
 8. A method as claimed in claim 7,wherein the sampling is carried out by means of single-phase containersfor reservoir fluid.
 9. A method as claimed in claim 1, wherein thesealing means comprises at least two axially spaced annular packerelements, located externally on a housing member located on a downstreamend portion of said pipe string within the area of said hydrocarboncarrying layer.
 10. A method as claimed in claim 1, further comprisingthe steps of sealing the pipe string as soon as said pipe string hasbeen filled with said reservoir fluid; completing said measuringoperations; and reopening said pipe string to allow the return of saidreservoir fluid to the hydrocarbon carrying layer in the groundformation.
 11. A method as claimed in claim 1, further comprising thestep of adding tracers to said reservoir fluid.
 12. A method as claimedin claim 11, wherein said adding step is performed by means of anadmixing accessory located in we a housing member.
 13. A method asclaimed in claim 1, further comprising the steps of separating thereservoir fluid from a piston drive medium within the pipe string;allowing the reservoir fluid to enter the pipe string; displacing apiston toward the piston drive medium, wherein the piston is containedin the pipe string and is displaced by the reservoir fluid when thepressure of the reservoir fluid is greater than the pressure of thepiston drive medium; stopping the displacement of the piston with aseat; moving the piston in the opposite direction of the displacement bymeans of the piston driving medium; returning the reservoir fluid to thehydrocarbon-carrying layer of the formation.
 14. A method as claimed inclaim 13, wherein the piston drive medium comprises water or N₂, andsaid seat is positioned at an upper security valve located on the pipestring.